Reticuloendothelial system (RES) function may be critical to survival following trauma. This project will investigate the influence of whole-body trauma and operative injury on RES liver and spleen phagocytic clearance of blood-borne particulate matter. RE depression exists following major surgery and trauma in both animals and man. The RE depression is mediated by depletion of an alpha-2-opsonic glycoprotein and restoration of opsonic activity is correlated with RE recovery. Non-surviving trauma patients have a persistent opsonic deficiency while surviving trauma patients manifest early RE recovery. RES depression is associated with an increment in pulmonary localization of particulate matter which may be of significance to respiratory disturbances following trauma. The opsonic glycoprotein from rat serum has been isolated and an immunoassay has been developed. The pure protein (I.V.) will stimulate RES phagocytosis and reverse post-trauma opsonic deficiency. Antiserum to opsonic protein will decrease RE function and impair resistance to trauma. With isotopic in vitro and in vivo methods, this project will: 1) evaluate the relationship between serum opsonin levels and RE function following surgery and trauma; 2) isolate and biochemically characterize the opsonic protein from human serum; 3) study the influence of post-trauma RE depression on the clearance of fibrin microaggregates, injured platelets, and colloids; 4) test opsonin therapy as a selective means to circumvent RE failure; 5) evaluate the influence of altered opsonin levels and RE function on survival following trauma; 6) develop an immunoassay for human alpha-2-opsonic protein and study this in patients after surgery and trauma; 7) correlate Re depression and impaired microaggregate clearance with pulmonary function. The coexistence following trauma of RES depression and an excess blood-borne microaggregates may present a precarious imblance between systemic defense and disease. Opsonic protein therapy may circumvent RE failure, and immunoreactive opsonin levels may provide a non-invasive technique to monitor RE function in surgical and trauma patients.